If Germany wants to make a naval build round 1, usually it will be 1 carrier + 2 transports OR 1 carrier, 1 destroyer and 1 submarine. Either way the total equals 30 IPCs.
The reason for this purchase is it gives Germany a lot of options on future moves.
A - The most obvious is a preparation for Sealion. You will need the loaded carrier plus other warships to protect the stack of transports you put there on round 2. Also, whatever ships Germany has will be used to clear the way for the German landings plus protect the transports if England scrambles, leaving more of your Luftwaffe to join in the London attack.
B - Secondly, you can use them to threaten Sealion even if you don’t plan to actually invade England. This keeps the UK on edge buying defensively which could give Italy some badly needed breathing room in the Med. If Germany can keep UK from putting more units in the Med for even just a couple of rounds, it could be just enough for Italy to get the upper hand.
C - A loaded carrier plus other warships will threaten any Allied fleet and cause the US in particular to invest in more warships to protect it’s transports if they want to stage by Gibraltar and think of approaching Europe.
D - You could use the German navy for an amphibious invasion of Leningrad when you decide to attack Russia. If you can take Leningrad in the same round that you first attack Russia, then you can replace the “Peace With Russia NO” with the “German Occupation of Leningrad NO” and not loose $5 when you attack Russia.
E - Another idea might be to send them into the Med to boost the Italian navy and help them get over the Allies there.
I’m sure there are other good uses that I just can’t think of right now. I guess since Germany buying a navy round 1 does at least threaten Sealion which may prevent England from running the Taranto raid, although I have seen them do it anyway even if Germany threatens Sealion. The point is, if the UK player you are playing with is bound and determined to wipe out the Italian navy, I don’t think your German G1 purchase will matter one way or the other.
That being said, while the naval purchase is most popular for Germany, they are not bound by it. There are many options. 2 bombers + 1 submarine OR 2 bombers + 1 tank are a couple of options. Another possibility is a Major IC to place in Romania in preparation for a major attack on Russia round 2 or 3.
As for the Taranto attack, the UK usually sends the following units:
1 carrier, 1 cruiser, 1 destroyer, 1 tac bomber from SZ 98 to SZ 97.
2 fighters, 1 bomber from London to SZ 97.
1 fighter from Malta to SZ 96.
1 fighter from Gibraltar to SZ 96.
The 2 fighters in SZ 96 to kill the Italian destroyer and transport. They will land on Malta.
The tac bomber from SZ 98 and strat bomber from London (assuming they survive) will land on Malta.
The 2 fighters from London will land on the carrier assuming they all survive.
The Taranto raid is pretty devastating to Italy but not necessarily game ending. Italy could recover and give UK a pretty good fight. At the very least, Italy is good for keeping the UK mostly occupied while Germany goes all out after Russia.
As for the 18 Russians in the east, there are a number of things you can do with them.
A - Move all 18 to Amur to temp Japan. In this case, they will probably get wiped out as Japan will probably take the bait. It will suck for Russia to lose all those guys and there will be nothing left to stop Japan from taking all those cheap territories. On the plus side, with Japan attacking, it will put Mongolia on Russia’s side and get them 6 more infantry. Also, Japan will be expending a lot of resources in this attack, which could slow it’s progress down south where the real money is for them.
B - Immediately start moving all those guys toward Moscow. With any luck, they will reach Moscow in time to protect the capital from the massive German assault. It does leave all the cheap territories in the east empty for Japan to take without a fight. However, Russia won’t lose more than 6 or 7 IPCs and the Mongolians will still join you.
C - Place some on Amur as a guard against Japanese aggression while holding some back for either a counter attack or to head back to Moscow. There can be any combination involved in this plan.
D - You can go aggressive. Fly your Moscow planes out to join them so those infantry will have a little offensive punch. If Japan withdraws troops from Manchuria and/or Korea and leave one or both weak enough, especially if Japan is very busy taking on India, Australia or maybe the US Navy, Russia could use their Siberian troops to take Korea and Manchuria. Depending on the situation, that could really weaken Japan financially. One thing though, if Russia is the one that first attacks Japan, the Mongolians will remain strict neutrals and will never join with the Soviets (unless an Axis power were to attack them directly).